High-energy lower extremity fractures have been associated with surgical site infection (SSI) and osteomyelitis rates ranging from approximately 14% to 60% in both military and civilian settings. The current standard for treatment of such fractures typically includes using metal implants (plates and screws or nails) for fracture fixation, which have the potential disadvantage of placing metal within a fracture site. These metal implants can serve as sites for bacterial adhesion and formation of a bacterial biofilm, where bacteria can remain sequestered from the body's immune system, resulting in surgical site infections.
Although the use of intravenous (IV) antibiotics as a prophylaxis against wound infection has become standard, infection rates in certain types of orthopedic trauma remain high. Systemic antibiotics may not reach the implant surface in sufficient concentration due to locally impaired circulation at the wound site, and bacterial biofilm formation can be very rapid. Biofilm based infections are not only resistant to systemic antibiotic therapy and the host immune system, they typically require additional surgery to remove the infected implant.
Locally delivered antibiotics hold promise for reducing SSIs, particularly those associated with high-energy fractures, as they can be used to deliver high concentrations of antibiotics where needed and prevent the development of biofilms on the implant surface. Multiple studies in animals have demonstrated that if an implant surface can be protected from colonization by bacteria for a period of time immediately after surgery, the rate of subsequent infection can be significantly reduced.
Surgeons have used a variety of products for local delivery of antibiotics, typically aminoglycosides and/or vancomycin, including polymethyl methacrylate (PMMA) cements, beads, gels, and collagen sponges. However, in certain situations, these antibiotic treatments are not practical, for example where they take up space at the site making wound closure difficult, and in other situations may also require a separate surgery for their removal.
Infections represent a major challenge in orthopedic or trauma surgery. Despite prophylactic measures like asepsis and antisepsis, the surgery site is still a site of access for local pathogens to become virulent and cause infections.
Coating an implantable device with a drug, such as an antibiotic, has been effective to reduce infection. However, given the large number, sizes, and shapes of implants and other medical devices, the regulatory, financial, and logistical burden of providing a coating for each device is enormous. The problem is amplified if one considers additional drugs to use in coatings such as analgesics, antineoplastic agents and growth promoting substances.